Air flow rate measuring device

Abstract

The present disclosure provides an air flow rate measuring including a casing and a sensor. The casing includes a main-bypass passage that defines an inlet and an outlet, a sub-bypass passage that branches off from the main-bypass passage at a branching area, and a guiding wall that changes, at a position upstream of the branching area, a flow direction of the passing air taken in from the inlet. The inlet and the guiding wall are arranged in an arranging direction along a flow direction of the intake air in the duct. The guiding wall includes an inlet side surface that faces the inlet and is not perpendicular to the arranging direction.

What is claimed is: 
     
       1. An air flow rate measuring device, comprising:
 a casing that is attached to a duct through which an intake air for an internal combustion engine flows along a first direction, the casing protruding into the duct along a second direction perpendicular to the first direction, a portion of the intake air passing through the casing as a passing air; and 
 a sensor that detects a flow rate of the passing air, the air flow rate measuring device measuring a flow rate of the intake air based on a detection result of the sensor, wherein 
 the casing includes:
 a main-bypass passage that defines an inlet to take in the intake air and an outlet to discharge the passing air taken in from the inlet; 
 a sub-bypass passage that branches off from the main-bypass passage at a branching area downstream of the inlet, the sensor being disposed in the sub-bypass passage; and 
 a guiding wall that is located downstream of the inlet along the first direction and changes, at a position upstream of the branching area, a flow direction of the passing air taken in from the inlet, 
 
 the guiding wall is not perpendicular to a plane which is parallel to the first and second directions, 
 the guiding wall includes an inlet side surface that faces the inlet, and 
 in a cross section of the guiding wall taken along both the first direction and a third direction direction perpendicular to the first and second directions, the inlet side surface is not perpendicular to the first direction. 
 
     
     
       2. The air flow rate measuring device according to  claim 1 , wherein
 the sub-bypass passage includes a curved portion that changes, at a position upstream of the sensor, a flow direction of the passing air taken in from the main-bypass passage, and 
 the casing includes a plurality of recessed portions that are recessed from an outer wall of the curved portion in a direction radially outward of the curved portion. 
 
     
     
       3. The air flow rate measuring device according to  claim 1 , wherein
 a direction of the intake air flowing through the outlet is angled with a direction of the intake air flowing through the inlet. 
 
     
     
       4. The air flow rate measuring device according to  claim 1 , wherein
 the sub-bypass passage includes a curved portion in the sub-bypass passage, 
 the curved portion changes, in the sub-bypass passage, a direction of the passing air, and 
 the sensor is disposed in the curved portion. 
 
     
     
       5. The air flow rate measuring device according to  claim 1 , wherein
 the guiding wall extends parallel to the second direction. 
 
     
     
       6. The air flow rate measuring device according to  claim 1 , wherein
 the inlet side surface is not perpendicular to the plane parallel to the first and second directions. 
 
     
     
       7. The air flow rate measuring device according to  claim 1 , wherein
 the main-bypass passage includes a guiding passage extending along the guiding wall and a passage extending from the guiding passage toward the outlet, 
 the sub-bypass passage includes an inflow sub-passage through which the passing air from the passage flows and an outflow sub-passage from which the passing air flows out toward the outlet, 
 the guiding wall separates the guiding passage from the inflow sub-passage in a direction such that the inflow sub-passage extends along the guiding passage, 
 the casing includes a sub-bypass wall that separates the outflow sub-passage from the inflow sub-passage such that the inflow sub-passage extends along the outflow sub-passage, and 
 the sensor is disposed in the inflow sub-passage to detect a flow rate of the passing air. 
 
     
     
       8. The air flow rate measuring device according to  claim 7 , wherein
 the sub-bypass wall extends along the guiding wall on a side of the inflow sub-passage opposite to the guiding passage, and 
 the sub-bypass wall protrudes toward the passage more than the guiding wall protrudes toward the passage. 
 
     
     
       9. The air flow rate measuring device according to  claim 7 , wherein
 the sub-bypass wall extends along the guiding wall on a side of the inflow sub-passage opposite to the guiding passage, and 
 the guiding wall protrudes toward the passage more than the sub-bypass wall protrudes toward the passage. 
 
     
     
       10. An air flow rate measuring device, comprising:
 a casing that is attached to a duct through which an intake air for an internal combustion engine flows, a portion of the intake air passing through the casing as a passing air; and 
 a sensor that detects a flow rate of the passing air, the air flow rate measuring device measuring a flow rate of the intake air based on a detection result of the sensor; and 
 an attachment surface that attaches the air flow rate measuring device to the duct, wherein 
 the casing includes:
 a main-bypass passage that defines an inlet to take in the intake air and an outlet to discharge the passing air taken in from the inlet; 
 a sub-bypass passage that branches off from the main-bypass passage at a branching area downstream of the inlet, the sensor being disposed in the sub-bypass passage; and 
 a guiding wall that faces the inlet along a first direction which is parallel to the attachment surface and that is disposed downstream of the inlet and changes, at a position upstream of the branching area, a flow direction of the passing air taken in from the inlet, 
 
 the main-bypass passage includes:
 a first curved portion that changes, in the main-bypass passage, a direction of the intake air taken in from the inlet, the first curved portion changing the direction of the intake air from the first direction to a second direction perpendicular to the attachment surface; and 
 a second curved portion that changes, at a position downstream of the first curved portion, a direction of the passing air, 
 
 the guiding wall is an outer circumferential surface of the first curved portion, and 
 an angle of the first curved portion is smaller than an angle of the second curved portion. 
 
     
     
       11. The air flow rate measuring device according to  claim 10 , wherein
 a direction of the intake air flowing through the outlet is angled with a direction of the intake air flowing through the inlet. 
 
     
     
       12. The air flow rate measuring device according to  claim 10 , wherein
 the angle of the second curved portion is larger than 90 degrees. 
 
     
     
       13. The air flow rate measuring device according to  claim 10 , wherein
 the main-bypass passage includes a guiding passage extending along the guiding wall and a passage extending from the guiding passage toward the outlet, 
 the sub-bypass passage includes an inflow sub-passage through which the passing air from the passage flows and an outflow sub-passage from which the passing air flows out toward the outlet, 
 the guiding wall separates the guiding passage from the inflow sub-passage in a direction such that the inflow sub-passage extends along the guiding passage, 
 the casing includes a sub-bypass wall that separates the outflow sub-passage from the inflow sub-passage such that the inflow sub-passage extends along the outflow sub-passage, and 
 the sensor is disposed in the inflow sub-passage to detect a flow rate of the passing air. 
 
     
     
       14. The air flow rate measuring device according to  claim 13 , wherein
 the sub-bypass wall extends along the guiding wall on a side of the inflow sub-passage opposite to the guiding passage, and 
 the sub-bypass wall protrudes toward the passage more than the guiding wall protrudes toward the passage. 
 
     
     
       15. The air flow rate measuring device according to  claim 13 , wherein
 the sub-bypass wall extends along the guiding wall on a side of the inflow sub-passage opposite to the guiding passage, and 
 the guiding wall protrudes toward the passage more than the sub-bypass wall protrudes toward the passage. 
 
     
     
       16. The air flow rate measuring device according to  claim 10 , wherein
 the guiding wall includes an inlet side surface that faces the inlet along a facing the first direction, and 
 the inlet side surface includes a slope surface that is tapered along a direction away from the inlet. 
 
     
     
       17. The air flow rate measuring device according to  claim 16 , wherein
 the guiding wall has a thickness along the first direction that increases as the slope surface approaches the inlet. 
 
     
     
       18. The air flow rate measuring device according to  claim 16 , wherein
 the sloped surface has a first side and a second side facing each other along a third direction perpendicular to the first direction and the second direction, 
 the first side is located between the second side and the inlet along the first direction, and 
 the guiding wall has a thickness along the first direction that increases from the second side toward the first side. 
 
     
     
       19. An air flow rate measuring device, comprising:
 an attachment portion that has an attachment surface, the attachment surface being attached to a duct through which an intake air for an internal combustion engine flows; 
 a casing through which a portion of the intake air passes as a passing air; and 
 a sensor that detects a flow rate of the passing air, the air flow rate measuring device measuring a flow rate of the intake air based on a detection result of the sensor, wherein 
 the casing includes:
 a main-bypass passage that defines an inlet to take in the intake air and an outlet to discharge the passing air taken in from the inlet; 
 a sub-bypass passage that branches off from the main-bypass passage at a branching area downstream of the inlet, the sensor being disposed in the sub-bypass passage; and 
 a guiding wall that is disposed downstream of the inlet and changes, at a position upstream of the branching area, a flow direction of the passing air taken in from the inlet, 
 
 the guiding wall has an inlet side surface that faces the inlet along a facing direction, 
 the inlet side surface has:
 a first side and a second side facing each other along a direction, the direction being parallel to the attachment surface and perpendicular to the facing direction; and 
 an intermediate portion located between the first side and the second side along the direction, and 
 
 the inlet side surface is tapered with respect to the direction with at least one of the first side or the second side being located between the intermediate portion and the inlet along the facing direction. 
 
     
     
       20. The air flow rate measuring device according to  claim 19 , wherein
 the intermediate portion is located between the first side and the second side along the facing direction. 
 
     
     
       21. The air flow rate measuring device according to  claim 19 , wherein
 both of the first side and the second side are located between the inlet and the intermediate portion.